U.S. patent application number 10/705362 was filed with the patent office on 2005-05-12 for flow control system for a gas turbine engine.
Invention is credited to Dalton, William H., Desai, Mihir C..
Application Number | 20050100447 10/705362 |
Document ID | / |
Family ID | 34435609 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050100447 |
Kind Code |
A1 |
Desai, Mihir C. ; et
al. |
May 12, 2005 |
Flow control system for a gas turbine engine
Abstract
A flow control system for controlling a variable displacement
pump including a metering valve in fluid communication with the
pump for metering an output of the pump. A regulating valve
receives a portion of the output of the pump as a bypass flow at a
first pressure, wherein an output of the regulating valve is at an
interim pressure. The interim pressure is substantially equal to an
average of the first pressure and a low reference pressure. An
actuator sets a displacement of the pump by acting on a piston
connected to a cam ring of the pump. The actuator receives the
interim pressure and, thereby, the output of the variable
displacement pump is determined.
Inventors: |
Desai, Mihir C.; (Yorba
Linda, CA) ; Dalton, William H.; (Amston,
CT) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP
P.O. BOX 55874
BOSTON
MA
02205
US
|
Family ID: |
34435609 |
Appl. No.: |
10/705362 |
Filed: |
November 11, 2003 |
Current U.S.
Class: |
417/220 |
Current CPC
Class: |
F04B 2201/1205 20130101;
F04B 49/002 20130101; F04C 2270/20 20130101; F04B 49/12 20130101;
F04B 1/07 20130101; F04B 2201/1213 20130101; F04C 14/226 20130101;
F04C 14/26 20130101; F04B 2201/1204 20130101; F04B 1/26
20130101 |
Class at
Publication: |
417/220 |
International
Class: |
F04B 049/00 |
Claims
What is claimed is:
1. A high-stability flow control system for controlling a variable
displacement pump, the flow control system comprising: a metering
valve in fluid communication with the pump for metering a pump
output; a regulating valve assembly for maintaining a pressure
differential across the metering valve, the regulating valve
assembly receiving a portion of the pump output of the pump as a
bypass flow at a first pressure, wherein a valve output from the
regulating valve assembly is at an interim pressure approximately
equal to an average of the first pressure and a low reference
pressure; and an actuator connected to the variable displacement
pump for setting a displacement of the variable displacement pump,
the actuator receiving the valve output for determining a setting
of the actuator and, thereby, the pump output.
2. A fuel metering unit as recited in claim 1, wherein a second
pressure within the actuator opposes the interim pressure.
3. A fuel metering unit as recited in claim 1, wherein the second
pressure is approximately equal to the interim pressure during
steady-state operation.
4. A fuel metering unit as recited in claim 1, further comprising a
filter in fluid communication with the output of the pump for
cleaning debris.
5. A fuel metering unit as recited in claim 1, further comprising a
first line connected between the metered output of the metering
valve and regulator valve assembly for dampening a response of the
regulating valve assembly.
6. A fuel metering unit as recited in claim 5, wherein the first
line is a static flow line.
7. A fuel metering unit as recited in claim 5, further comprising
an orifice in the first line.
8. A fuel metering unit as recited in claim 1, further comprising a
second line connected between the regulating valve assembly and cam
actuator for providing the interim pressure to the cam
actuator.
9. A fuel metering unit as recited in claim 1, wherein the actuator
includes a piston connected to a movable cam ring of the pump.
10. A fuel metering unit for controlling a variable displacement
pump wherein the variable displacement pump receives fuel at a low
reference pressure and produces an output at an elevated pressure,
the fuel metering unit comprising: first means in fluid
communication with the pump for metering the output of the pump;
second means in fluid communication with the first means for
maintaining a substantially constant pressure differential across
the third means, and producing an interim pressure approximately
equal to an average of the elevated pressure and the low reference
pressure; third means operatively connected to the variable
displacement pump for controlling the output of the pump, a setting
of the third means being based upon a difference between the
interim pressure and an opposing pressure; and fuel lines connected
between the output of the variable displacement pump and the third
means for providing the opposing pressure to the third means.
11. A fuel metering unit as recited in claim 10, wherein the fuel
lines are also connected to the low reference pressure such that
the interim pressure and the opposing pressure are substantially
equal during steady-state operations.
12. A fuel metering unit as recited in claim 10, wherein the first
means is a metering valve.
13. A fuel metering unit as recited in claim 10, wherein the second
means is a regulating valve.
14. A fuel metering unit as recited in claim 10, wherein the third
means is a cam actuator.
15. A fuel metering unit as recited in claim 10, further comprising
a filter in fluid communication with the output of the pump for
cleaning debris.
16. A fuel metering unit as recited in claim 10, further comprising
a first line connected between the metered output of the first
means and third means for dampening a response of the third
means.
17. A fuel metering unit as recited in claim 15, wherein the first
line is a static flow line.
18. A fuel metering unit as recited in claim 15, further comprising
an orifice in the first line.
19. A fuel metering unit as recited in claim 10, further comprising
a second line connected between the third means and the second
means for dampening a response of the second means.
20. A method for metering a variable displacement pump that
provides fuel to an engine, the method comprising the steps of:
receiving fuel at a low reference pressure into the variable
displacement pump; pumping the fuel through the pump such that an
output of the pump is at an elevated pressure; metering the output
of the variable displacement pump with a metering valve; creating a
spill return flow from the output of the variable displacement pump
to allow for quick response when additional fuel is required by the
engine; regulating a pressure differential across the metering
valve with a regulating valve, the regulating valve being in fluid
communication with the spill return flow, wherein the regulating
valve generates an interim pressure substantially equal to an
average of the spill return and the low reference pressure; and
adjusting a displacement of the pump with a cam actuator connected
to a cam ring of the variable displacement pump for adjusting the
output, wherein the cam actuator receives the interim pressure to
determine a setting of the cam actuator.
21. A method as recited in claim 20, further comprising the step of
providing a second pressure to the cam actuator in opposition to
the interim pressure.
22. A method as recited in claim 20, further comprising the step of
damping a response of the regulating valve by inputting a metered
output of the metering valve to the regulating valve.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The subject invention is directed generally to a system for
regulating fluid flow, and more particularly, to a system for
regulating the flow of liquid fuel from a variable displacement
pump to a gas turbine by utilizing bypass flow.
[0003] 2. Background of the Related Art
[0004] Fixed delivery fuel pumps have often been over-sized to
provide excessive fuel flow capacity in order to insure adequate
supply to the associated engine. Consequently, under many operating
conditions, large amounts of pressurized fuel are returned to the
pump inlet for recirculation. The return and recirculation results
in significant fuel heating due to additional energy being put into
the fuel which is subsequently turned into heat as the pressure
drops in the recirculation path. In modem designs, fuel heating is
a critical issue because the fuel is typically used as a heat
exchanger to maintain proper operating temperature. Other methods
of heat exchange are undesirable because of the associated size,
weight and cost. Such concerns are magnified in modem engines
because the fuel pumps also need to supply fuel to engine
geometries. For example, modem mid to large class engines utilize
linear pistons as guide vanes. The linear pistons require a
significant source of fuel to slew. This slewing is a transient
event that can unacceptably starve the supply of fuel to the
engine.
[0005] Variable displacement fuel pumps have partially overcome the
drawbacks of fixed delivery pumps by being able to vary the amount
of fuel output. By varying the fuel output, the fuel delivered more
closely matches engine demand. Thus, the recirculated flow, along
with the heat generated thereby, is reduced. Variable displacement
fuel pumps are known in the art as disclosed in U.S. Pat. No.
5,833,438 to Sunberg, the disclosure of which is herein
incorporated by reference in its entirety. A variable displacement
pump typically includes a rotor having a fixed axis and pivoting
cam ring. Controlling the position of the cam ring with respect to
the rotor controls the output of the pump. The output flow may be
controlled by a torque motor operated servo valve. However, the
engine operating conditions often include transients such as those
caused by engine actuator slewing, start-up and the like as would
be appreciated by those of ordinary skill in the pertinent art.
Under such rapidly varying operating conditions, prior art pump
control systems have been unable to respond quickly and adequately.
Moreover, many prior art pump control systems lack the required
stability to reliably provide fuel to the engine. So despite the
advances of the state of the art, variable displacement pumps are
lacking in stability and still do not respond quickly enough to
varying engine demands. As a result, poor performance and excess
fuel flow are still common.
[0006] Examples of variable displacement pump control arrangements
are disclosed in U.S. Pat. No. 5,716,201 to Peck et al. and U.S.
Pat. No. 5,715,674 to Reuter et al., the disclosures of which are
herein incorporated by reference in their entirety. These pump
control systems attempt to maintain accurate fuel flow throughout
the range of engine operating conditions. However, as noted above,
such systems still contain inadequacies such as complexity.
Moreover, such systems can only achieve adequate bandwidth by
delivering excessive fuel which must be recirculated. It is also
undesirable for pump control systems to include sophisticated
electronics and numerous additional components that undesirably
increase costs and complexity.
[0007] In view of the above, it would be desirable to provide a
flow control system which has a simple design for quickly
regulating the output flow of a variable displacement pump with
stability and without the associated drawbacks of the prior
art.
SUMMARY OF THE INVENTION
[0008] In one embodiment, the subject invention is directed to a
flow control system for controlling a variable displacement pump
including a metering valve in fluid communication with the pump for
metering an output of the pump. A regulating valve for maintaining
a pressure differential across the metering valve receives a
portion of the output of the pump as a bypass flow at a first
pressure, wherein an output of the regulating valve is at an
interim pressure, wherein the interim pressure is equal to an
approximate average of the first pressure and a low reference
pressure. An actuator sets a displacement of the pump by acting on
a piston connected to a cam ring of the pump. The setting of the
actuator is determined by a differential between the interim
pressure and a second portion of the output of the pump at the
first pressure.
[0009] It is an object of the present disclosure to increase the
fuel metering unit response while maintaining acceptable stability
at all operating conditions.
[0010] It is another object to provide a hydromechanical fuel
metering unit for a variable displacement pump. It is still another
object to provide a fuel metering unit that achieves quick and
accurate response to dynamic flow conditions.
[0011] In another embodiment, the subject invention is directed to
a method for metering a variable displacement pump that provides
fuel to an engine, the method includes the steps of receiving fuel
at a low reference pressure into the variable displacement pump,
pumping the fuel through the pump such that an output of the pump
is at an elevated pressure, metering the output of the variable
displacement pump with a metering valve, creating a spill return
flow from the output of the variable displacement pump to allow for
quick response when additional fuel is required by the engine,
regulating a pressure differential across the metering valve with a
regulating valve. The regulating valve is in fluid communication
with the spill return flow to generate an interim pressure
substantially equal to an average of the spill return and the low
reference pressure. The method also includes the step of adjusting
a displacement of the pump with a cam actuator connected to a cam
ring of the variable displacement pump for adjusting the output,
wherein the cam actuator receives the interim pressure to determine
a setting of the cam actuator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] So that those having ordinary skill in the art to which the
subject invention appertains will more readily understand how to
make and use the same, reference may be had to the Sole FIGURE
wherein:
[0013] The Sole FIGURE is a schematic representation of a flow
control system constructed in accordance with the subject
invention.
DETAILED DESCRIPTION OF PREFERRED EMBDOMENTS
[0014] Referring now to the Sole FIGURE, there is illustrated a
schematic representation of a flow control system in accordance
with the subject invention which is designated generally by
reference numeral 10. For clarity throughout the following
description, arrows are shown within the lines of system 10 to
indicate the direction in which the fuel flows and an annotated
letter "P" is shown to indicate a pressure at certain locations.
All relative descriptions herein such as left, right, up, and down
are with reference to the system 10 as shown in the Sole FIGURE and
not meant in a limiting sense. Additionally, for clarity common
items such as filters and shut off solenoids have not been included
in the Sole FIGURE. The system 10 maintains the output flow of a
variable vane displacement pump 12 to provide fast response to
engine needs in a stable manner yet excessive complexity is
avoided.
[0015] The pump 12 includes a rotor 14 and a pivoting cam ring 16.
For a detailed description of a variable displacement vane pump,
see U.S. Patent Application Publication No. 2002/0103849 published
on Jun. 5, 2003 which is incorporated herein by reference in its
entirety. The pump 12 receives fuel flow at an inlet pressure
P.sub.AF, and delivers fuel flow at an output pressure P.sub.F. A
piston 18 is operatively connected to the cam ring 16 to control
the position of the cam ring 16 relative to the rotor 14 and,
thereby, vary the output flow of the pump 12. A cam actuator
assembly 20 positions the piston 18 as described below. It should
be appreciated by those of ordinary skill in the art that other
types of actuators similarly and differently arranged would perform
this same function and are, therefore, considered mere design
choices well within the scope of the subject invention as claimed.
The maximum flow setting of the pump 12 occurs when the piston 18
is moved the maximum distance to the left.
[0016] A feedback line 21 in fluid communication with the output of
the pump 12 provides fuel at pressure P.sub.1W to a line 29
connected to an inlet 22 of the cam actuator 20. Orifices 24 and 26
limit the flow into line 29. The pressure in line 29 is
approximately equal to P.sub.1W+P.sub.AF divided by two, and
designated as P.sub.I1 in the Sole FIGURE. It will be appreciated
by those of ordinary skill in the art that the pressure at P.sub.1W
will be substantially equal to the pressure P.sub.F. The feedback
line 21 also provides fuel at pressure P.sub.1W to other locations
not shown such as the engine geometry, main metering valve and
bleed band servos (not shown) as required. Line 29 also connects to
low reference pressure P.sub.AF. Another inlet 28 of the cam
actuator 20 receives fuel at an interim pressure P.sub.I2 as will
be described hereinbelow.
[0017] A housing 23 of the cam actuator 20 retains the piston 18
for dividing the interior of the housing 23. A coiled spring 30
biases the piston 18. Within the housing 23, the pressure on the
right side of the piston 18 is approximately equal to the average
of P.sub.1W and P.sub.AF. The combination of the pressure
differential between the right and left sides of the housing 23
together with the sizing of a spring 30 act to position the piston
18 within the cam actuator 20. The cam ring 16 moves
correspondingly and the output of the pump 12 varies. Preferably,
the spring 30 is sized and configured to position the piston 18 at
maximum flow for start-up of the pump 12. Throughout system 10,
springs are sized as a function of the product of piston area and
fuel pressure as would be appreciated by those of ordinary skill in
the art and therefore not further described herein.
[0018] The output of the pump 12 passes through a wash filter 32
for cleaning debris prior to entering a main metering valve 34 and
line 21. The main metering valve 34 is disposed between the pump 12
and engine (not shown) for providing fuel to the engine at a
selected rate and pressure P.sub.M. The main metering valve 34
insures that P.sub.F is greater than P.sub.M by some pre-selected,
substantially constant value. Suitable main metering valves 34 are
well known in the prior art and therefore not further described
herein. The preferred metering valve 34 performs the function of
selectively varying the amount of fuel passing therethrough. The
main metering valve 34 receives fuel at pressure P.sub.F and the
fuel exits at pressure P.sub.M.
[0019] A line 35 connects the output of the pump 12 to a bypassing
pressure regulator valve assembly 36. The flow in line 35 is
referred to as the spill return flow at Pressure P.sub.F. The
regulator valve assembly 36 includes a housing 38 defining an
interior with a spring-biased spool 40 operatively disposed
therein. A left face of the spool 40 has fuel at pressure P.sub.F
there against. A metering head adjustment screw 42 is attached to
the spool 40 for calibrating the position of the spool 40 within
the regulator valve assembly 36 during set up. The housing 38
defines an inlet 44 connected to line 35 for receiving fuel at
pressure P.sub.F. Another inlet 46 of the housing 38 receives fuel
at pressure P.sub.M from static flow line 37 to dampen the motion
of the spool 40. An orifice 48 is disposed in the line 37 for
dampening. The housing 38 also defines a restricting outlet 50 for
the fuel to exit from the regulator valve assembly 36. The outlet
50 is in fluid communication with the inlet 28 of the pump 12 via
line 51. Line 51 also connects the low reference pressure P.sub.AF,
wherein an orifice 52 limits the flow to the low reference pressure
P.sub.AF. The pressure within line 51 is approximately equal to the
average of P.sub.F and P.sub.AF, hereinafter designated the interim
pressure P.sub.I2. The combination of the pressure differential
between P.sub.F on the left side of the housing 40 and P.sub.M on
the right plus the spring-biasing of the spool 40 ultimately
positions the spool 40.
[0020] During steady-state operation, the left side of regulator
valve assembly 36 and the right side of the cam actuator 20 are at
approximately the same pressure. The recirculation flow through the
regulator valve assembly 36 is maintained at a low level by the
spool 40 partially blocking the outlet 50 yet the system 10 can
rapidly and sufficiently respond to transient events. In the
preferred embodiment, the spool 40 within the regulator valve
assembly 36 is maintained substantially at a nominal position
during normal operation. In most modem engines, the variation in
fuel demand as a result of running the engine is relatively minor
compared to that associated with the slewing of engine
geometries.
[0021] When a transient event occurs, the pump 12 must produce more
fuel rapidly. For example, a transient event would be an actuator
motion by utilization of the slewing source at pressure P.sub.1W in
line 21. Increased demand by the transient event causes the main
metering valve 34 to respond by opening to immediately increase
flow to the engine and starts a chain of events which leads to an
increase in the output of the pump 12. The pump 12 cannot
immediately respond with increased displacement so the incremental
demand comes from diminished spill return flow in line 35. As a
result, the pressure P.sub.M increases and the Pressure P.sub.F
decreases (i.e., a drop of the pressure differential
(P.sub.F-P.sub.M) across the main metering valve 34). The regulator
valve assembly 36 senses the pressure differential drop and the
spool 40 strokes to the left. The pressure in the outlet 50 is
decreased and, in turn, the pressure into the left side of the cam
actuator 20 drops. The decrease in pressure of the left side of the
cam actuator 20 causes the piston 18 to stroke to the left. When
the piston 18 strokes to the left, the output of the pump 12
increases. The increased pump output raises the pressure P.sub.F
until the pressure differential across the main metering valve 34
returns to the nominal steady-state level and the steady-state
condition is reattained.
[0022] In the alternative, when a transient event occurs where the
pump 12 must rapidly decrease the output to prevent excessive
recirculation, the main metering valve 20 responds by closing to
decrease flow to the engine and starts a chain of events which
leads to a decrease in the output of the pump 12. The pump 12
cannot immediately respond with decreased displacement so the
decreased demand results in a decrease of pressure P.sub.M and an
increase in Pressure P.sub.F (i.e., a rise of the pressure
differential (P.sub.F-P.sub.M) across the main metering valve 34)
to allow the system 10 to immediately respond. The regulator valve
assembly 36 senses the pressure differential rise and the spool 40
strokes to the right. As a result, the pressure in the outlet 50 is
increased and, in turn, the pressure into the left side of the cam
actuator 20 rises. The rise in pressure of the left side of the cam
actuator 20 causes the piston 18 to stroke to the right. When the
piston 18 strokes to the right, the output of the pump 12 decreases
until the pressure differential (P.sub.F-P.sub.M) across the main
metering valve 34 returns to the nominal steady-state level with
the spool 40 substantially at a nominal position with the regulator
valve assembly 36.
[0023] In summary, the regulator valve assembly 36 is used to
minimize the recirculation flow, while allowing the system 10 to
respond quickly to transient demands. The recirculation flow is
regulated and the position of the spool 40 is at a substantially
nominal position during steady-state operation. Pressures
substantially equal to the average of the low reference pressure
and output pressure of the pump are utilized to set the regulator
valve and cam actuator.
[0024] While the subject invention has been described with respect
to preferred embodiments, those skilled in the art will readily
appreciate that various changes and/or modifications can be made to
the invention without departing from the spirit or scope of the
invention as defined by the appended claims.
* * * * *